functions of MATLAB are similar to C language function or FORTRAN subroutines. Functions are basically a programs stored as text in files having names with default extension of MATLAB that is .m file (dot m file). These are known as m files. Each dot m file contains a MATLAB function. MATLAB has collection of various functions for specific field, algorithms and combine together functions of MATLAB can lead a large number of small functions or files. One major difference between MATLAB and other traditional languages used by researchers is functions of MATLAB can be used interactively in simple manner. In addition to providing the support for interactive calculation. In MATLAB , it is very convenient to debug or find a particular bug in large as well as small function. We can easily write in small parts so that it is easy to debug the particular function when it revokes some error while performing the execution of algorithm. Functions of MATLAB have two basic parameters for input and output. Writing functions in MATLAB is a simple as we can write content in notepad. Function defines the output parameter list in the left side and input parameter list in the right side. Outputs and input parameters are enclosed in square brackets as per defines in syntax of MATLAB. Calling of function of MATLAB is very useful and it can be created while omitting the output arguments of function definition. The input and output variables can be scalar, vectors, matrices and strings. One main thing which is the most important should be kept in mind while programming MATLAB does not have ability to distinguish between variables types until some calculation or operation involving the variables is performed. Every toolbox of MATLAB has some functions that are predefined for user. Here are the some examples of functions available in image processing toolbox are imshow ,imread ,imwrite, rgb2gray,im2bw and many more.